AWS Serverless

Introduction

This is an example of how to set up a serverless framework function within AWS

Setup

Within AWS there are example templates for each piece of the infrastructure. For this we need to create a

• S3 Bucket to hold the code
• IAM::Role to describe the permissions
• Lambda The function to run
• Bucket Policy This grants access from the bucket to the lambda function

Templates

Here are the templates I used. I have highlighted where they differ from the provided examples

Stack cowsay-bucket

S3 Bucket

Example can be found here
This needs to be in its own stack and create prior to the other resources.

{
    "Resources": {
        "cowsayBucket": {
            "Type": "AWS::S3::Bucket",
            "Properties": {
                "BucketName": "cowsayBucket"
            }
        }
    }
}

Stack cowsay-lambda

This stack or group of resources holds the lamda, bucket policy and role. The lambda function references the bucket created above.

IAM::Role

Example can be found here

{
    "Resources": {
        "cowsayIamRole": {
            "Type": "AWS::IAM::Role",
            "Properties": {
                "AssumeRolePolicyDocument": {
                    "Version": "2012-10-17",
                    "Statement": [
                        {
                            "Effect": "Allow",
                            "Principal": {
                                "Service": [
                                    "lambda.amazonaws.com"
                                ]
                            },
                            "Action": [
                                "sts:AssumeRole"
                            ]
                        }
                    ]
                },
                "Path": "/",
                "Policies": [
                    {
                        "PolicyName": "root",
                        "PolicyDocument": {
                            "Version": "2012-10-17",
                            "Statement": [
                                {
                                    "Effect": "Allow",
                                    "Action": [
                                        "logs:*"
                                    ],
                                    "Resource": "arn:aws:logs:*:*:*"
                                }
                            ]
                        }
                    }
                ]
            }
        }
    }
}

Lambda Function

Example can be found here

{
    "Resources": {
        "cowsayLambda": {
            "Type": "AWS::Lambda::Function",
            "Properties": {
                "Code": {
                    "S3Bucket": "cowsaybucket",
                    "S3Key": "cowsay.zip"
                },
                "Handler": "index.handler",
                "Runtime": "nodejs14.x",
                "Role": {
                    "Fn::GetAtt": [
                        "cowsayIamRole",
                        "Arn"
                    ]
                }
            }
        }
    }
}

Adding the Role to the Lambda

Now we have the base templates we need to add properties to allow them to interact

{
    "Resources": {
        "cowsayBucket": {
            "Type": "AWS::S3::Bucket",
            "Properties": {
                "BucketName": "cowsayBucket"
            }
        },
        "Role": {
            "Ref": "cowsayIamRole"
        }
    }
}

Bucket Policy

We need to allow lambda function access to the bucket. We do this with a the bucket

{
    "Resources": {
        "cowsayBucketPolicy": {
            "Type": "AWS::S3::BucketPolicy",
            "Properties": {
                "Bucket": "cowsaybucket",
                "PolicyDocument": {
                    "Statement": [
                        {
                            "Effect": "Allow",
                            "Principal": {
                                "Service": "serverlessrepo.amazonaws.com"
                            },
                            "Action": "s3:GetObject",
                            "Resource": "arn:aws:s3:::cowsaybucket/*",
                            "Condition": {
                                "StringEquals": {
                                    "aws:SourceArn": {
                                        "Fn::GetAtt": [
                                            "cowsayLambda",
                                            "Arn"
                                        ]
                                    }
                                }
                            }
                        }
                    ]
                }
            }
        }
    }
}

The Code

Do do this we

• Create a node js package
• Create a function
• Create a template to run it locally

Create a node js package

Just a straight forward package

{
  "name": "cowsay",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "cowsay": "^1.4.0"
  }
}

Create a function

const cowsay = require('cowsay');
exports.handler = function(event, context) {
    // Get a cow from cowsay!
    let cow = cowsay.say({
        text: "I'm a lambda moooodule",
        e: "oO",
        T: "U "
    });
// Replace line breaks to HTML line breaks
    cow = cow.replace(/[\n|\r|\n\r]/g, '<br />');
// Create the HTML
    var html = '<html><head><title>Cowsay Lambda!</title></head>' + 
        `<body><h1>Welcome to Cowsay Lambda!</h1>${cow}</body></html>`;
    
    // New Source 1
            
    // Return the HTML response
    context.succeed(html);
};

Create a template to run it locally

See here for documentation.

AWSTemplateFormatVersion: '2010-09-09'
Transform: 'AWS::Serverless-2016-10-31'
Description: An AWS Serverless Specification template describing your function.
Resources:
  myfirstlambda:
    Type: 'AWS::Serverless::Function'
    Properties:
      Handler: index.handler
      Runtime: nodejs14.x
      CodeUri: .
      Description: ''
      MemorySize: 128
      Timeout: 3

We need to create a function. We create a package and function